Niacin prodrugs and deuterated versions thereof

ABSTRACT

The invention relates to prodrugs of niacin and their use in pharmaceutical composition and therapeutic treatment of disease.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/262,292, filed on Nov. 18, 2009. The entire teachings of the above application are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Many current medicines suffer from poor absorption, distribution, metabolism and/or excretion (ADME) properties that prevent their wider use. Poor ADME properties are also a major reason for the failure of drug candidates in clinical trials. While formulation technologies and prodrug strategies can be employed in some cases to improve certain ADME properties, these approaches often fail to address the underlying ADME problems that exist for many drugs and drug candidates. One such problem is rapid metabolism that causes a number of drugs, which otherwise would be highly effective in treating a disease, to be cleared too rapidly from the body. A possible solution to rapid drug clearance is frequent or high dosing to attain a sufficiently high plasma level of drug. This, however, introduces a number of potential treatment problems such as poor patient compliance with the dosing regimen, side effects that become more acute with higher doses, and increased cost of treatment.

In some select cases, a metabolic inhibitor will be co-administered with a drug that is cleared too rapidly. Such is the case with the protease inhibitor class of drugs that are used to treat HIV infection. The FDA recommends that these drugs be co-dosed with ritonavir, an inhibitor of cytochrome P450 enzyme 3A4 (CYP3A4), the enzyme typically responsible for their metabolism (see Kempf, D. J. et al., Antimicrobial agents and chemotherapy, 1997, 41(3): 654-60). Ritonavir, however, causes adverse effects and adds to the pill burden for HIV patients who must already take a combination of different drugs. Similarly, the CYP2D6 inhibitor quinidine has been added to dextromethorphan for the purpose of reducing rapid CYP2D6 metabolism of dextromethorphan in a treatment of pseudobulbar affect. Quinidine, however, has unwanted side effects that greatly limit its use in potential combination therapy (see Wang, L et al., Clinical Pharmacology and Therapeutics, 1994, 56(6 Pt 1): 659-67; and FDA label for quinidine at www.accessdata.fda.gov).

In general, combining drugs with cytochrome P450 inhibitors is not a satisfactory strategy for decreasing drug clearance. The inhibition of a CYP enzyme's activity can affect the metabolism and clearance of other drugs metabolized by that same enzyme. CYP inhibition can cause other drugs to accumulate in the body to toxic levels.

A potentially attractive strategy for improving a drug's metabolic properties is deuterium modification. In this approach, one attempts to slow the CYP-mediated metabolism of a drug by replacing one or more hydrogen atoms with deuterium atoms. Deuterium is a safe, stable, non-radioactive isotope of hydrogen. Compared to hydrogen, deuterium forms stronger bonds with carbon. In select cases, the increased bond strength imparted by deuterium can positively impact the ADME properties of a drug, creating the potential for improved drug efficacy, safety, and/or tolerability. At the same time, because the size and shape of deuterium are essentially identical to those of hydrogen, replacement of hydrogen by deuterium would not be expected to affect the biochemical potency and selectivity of the drug as compared to the original chemical entity that contains only hydrogen.

Over the past 35 years, the effects of deuterium substitution on the rate of metabolism have been reported for a very small percentage of approved drugs (see, e.g., Blake, Mich. et al, J Pharm Sci, 1975, 64:367-91; Foster, A B, Adv Drug Res 1985, 14:1-40 (“Foster”); Kushner, D J et al, Can J Physiol Pharmacol 1999, 79-88; Fisher, M B et al, Curr Opin Drug Discov Devel, 2006, 9:101-09 (“Fisher”)). The results have been variable and unpredictable. For some compounds deuteration caused decreased metabolic clearance in vivo. For others, there was no change in metabolism. Still others demonstrated increased metabolic clearance. The variability in deuterium effects has also led experts to question or dismiss deuterium modification as a viable drug design strategy for inhibiting adverse metabolism (see Foster at p. 35 and Fisher at p. 101).

The effects of deuterium modification on a drug's metabolic properties are not predictable even when deuterium atoms are incorporated at known sites of metabolism. Only by actually preparing and testing a deuterated drug can one determine if and how the rate of metabolism will differ from that of its non-deuterated counterpart. See, for example, Fukuto et al. (J. Med. Chem. 1991, 34, 2871-76). Many drugs have multiple sites where metabolism is possible. The site(s) where deuterium substitution is required and the extent of deuteration necessary to see an effect on metabolism, if any, will be different for each drug.

This invention relates to novel niacin prodrugs and pharmaceutically acceptable salts thereof. This invention also provides compositions comprising a compound of this invention and the use of such compositions in methods of treating diseases and conditions that are beneficially treated by administering niacin.

Niacin, also known as vitamin B3 or nicotinic acid, reduces serum levels of total cholesterol, triglyceride, and low-density lipoprotein and increases serum levels of high-density lipoproteins. One of the major side effects of niacin administration is skin flushing.

Recently, laropiprant, known to minimize flushing due to niacin administration, has been combined with niacin in an extended-release formulation (MK-524A). This combination has been approved in Europe for the treatment of hypercholesterolemia and dyslipidemia under the trademark Tredaptive®. However, approval of MK-524A in patients with heterozygous familial hypercholesterolemia had not been obtained. Phase III clinical trials of MK-524A for the treatment of atherosclerosis are ongoing.

Despite the beneficial activities of niacin, there is a continuing need for compositions or derivatives thereof that provide the beneficial effects of niacin, but reduce or avoid the adverse side effects.

DEFINITIONS

The term “treat” means decrease, suppress, attenuate, diminish, arrest, or stabilize the development or progression of a disease (e.g., a disease or disorder delineated herein), lessen the severity of the disease or improve the symptoms associated with the disease.

“Disease” means any condition or disorder that damages or interferes with the normal function of a cell, tissue, or organ.

The term “alkyl” refers to a monovalent saturated hydrocarbon group. C₁-C₆ alkyl is an alkyl having from 1 to 6 carbon atoms. An alkyl may be linear or branched. Examples of alkyl groups include methyl; ethyl; propyl, including n-propyl and isopropyl; butyl, including n-butyl, isobutyl, sec-butyl, and t-butyl; pentyl, including, for example, n-pentyl, isopentyl, and neopentyl; and hexyl, including, for example, n-hexyl and 2-methylpentyl.

The term “cycloalkyl” refers to a monocyclic or bicyclic monovalent saturated or non-aromatic unsaturated hydrocarbon ring system. The term “C₃-C₁₀ cycloalkyl” refers to a cycloalkyl wherein the number of ring carbon atoms is from 3 to 10. Examples of C₃-C₁₀ cycloalkyl include C₃-C₆ cycloalkyl. Bicyclic ring systems include fused, bridged, and spirocyclic ring systems. More particular examples of cycloalkyl groups include, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cis- and trans-decalinyl, norbornyl, and spiro[4.5]decanyl.

The term “heterocycloalkyl” refers to a monocyclic or bicyclic monovalent saturated or non-aromatic unsaturated ring system wherein from 1 to 4 ring atoms are heteroatoms independently selected from the group consisting of O, N and S. The term “3 to 10-membered heterocycloalkyl” refers to a heterocycloalkyl wherein the number of ring atoms is from 3 to 10. Examples of 3 to 10-membered heterocycloalkyl include 3 to 6-membered heterocycloalkyl. Bicyclic ring systems include fused, bridged, and spirocyclic ring systems. More particular examples of heterocycloalkyl groups include azepanyl, azetidinyl, aziridinyl, imidazolidinyl, morpholinyl, oxazolidinyl, oxazolidinyl, piperazinyl, piperidinyl, pyrazolidinyl, pyrrolidinyl, quinuclidinyl, and thiomorpholinyl.

The term “heteroaryl” refers to a monovalent aromatic monocyclic or bicyclic ring system wherein at least one ring atoms is a heteroatom independently selected from the group consisting of O, N and S. The term 5-membered heteroaryl refers to a heteroaryl wherein the number of ring atoms is 5. Examples of 5-membered heteroaryl groups include pyrrolyl, pyrazolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, oxadiazolyl, thiadiazolyl, furazanyl, imidazolinyl, and triazolyl. Bicyclic heteroaryl groups are typically 8, 9 or 10 membered. Examples include benzimidazolyl, benzothienyl, benzofuranyl, indolyl, quinolinyl, benzotriazolyl, benzothiazolyl, benzoxazolyl, benzimidazolyl, isoquinolinyl, indolyl, isoindolyl, or benzisoxazolyl.

It will be recognized that some variation of natural isotopic abundance occurs in a synthesized compound depending upon the origin of chemical materials used in the synthesis. Thus, a preparation of niacin will inherently contain small amounts of deuterated isotopologues. The concentration of naturally abundant stable hydrogen and carbon isotopes, notwithstanding this variation, is small and immaterial as compared to the degree of stable isotopic substitution of compounds of this invention. See, for instance, Wada, E et al., Seikagaku, 1994, 66:15; Gannes, L Z et al., Comp Biochem Physiol Mol Integr Physiol, 1998, 119:725.

In the compounds of this invention any atom not specifically designated as a particular isotope is meant to represent any stable isotope of that atom. Unless otherwise stated, when a position is designated specifically as “H” or “hydrogen”, the position is understood to have hydrogen at its natural abundance isotopic composition. Also unless otherwise stated, when a position is designated specifically as “D” or “deuterium”, the position is understood to have deuterium at an abundance that is at least 3340 times greater than the natural abundance of deuterium, which is 0.015% (i.e., at least 50.1% incorporation of deuterium).

The term “isotopic enrichment factor” as used herein means the ratio between the isotopic abundance and the natural abundance of a specified isotope.

In other embodiments, a compound of this invention has an isotopic enrichment factor for each designated deuterium atom of at least 3500 (52.5% deuterium incorporation at each designated deuterium atom), at least 4000 (60% deuterium incorporation), at least 4500 (67.5% deuterium incorporation), at least 5000 (75% deuterium), at least 5500 (82.5% deuterium incorporation), at least 6000 (90% deuterium incorporation), at least 6333.3 (95% deuterium incorporation), at least 6466.7 (97% deuterium incorporation), at least 6600 (99% deuterium incorporation), or at least 6633.3 (99.5% deuterium incorporation).

The term “isotopologue” refers to a species that differs from a specific compound of this invention only in the isotopic composition thereof.

The term “compound,” when referring to a compound of this invention, refers to a collection of molecules having an identical chemical structure, except that there may be isotopic variation among the constituent atoms of the molecules. Thus, it will be clear to those of skill in the art that a compound represented by a particular chemical structure containing indicated deuterium atoms, will also contain lesser amounts of isotopologues having hydrogen atoms at one or more of the designated deuterium positions in that structure. The relative amount of such isotopologues in a compound of this invention will depend upon a number of factors including the isotopic purity of deuterated reagents used to make the compound and the efficiency of incorporation of deuterium in the various synthesis steps used to prepare the compound. However, as set forth above the relative amount of such isotopologues in toto will be less than 49.9% of the compound. In other embodiments, the relative amount of such isotopologues in toto will be less than 47.5%, less than 40%, less than 32.5%, less than 25%, less than 17.5%, less than 10%, less than 5%, less than 3%, less than 1%, or less than 0.5% of the compound.

The invention also provides salts of the compounds of the invention.

A salt of a compound of this invention is formed between an acid and a basic group of the compound, such as an amino functional group, or a base and an acidic group of the compound, such as a carboxyl functional group. According to another embodiment, the compound is a pharmaceutically acceptable acid addition salt.

The term “pharmaceutically acceptable,” as used herein, refers to a component that is, within the scope of sound medical judgment, suitable for use in contact with the tissues of humans and other mammals without undue toxicity, irritation, allergic response and the like, and are commensurate with a reasonable benefit/risk ratio. A “pharmaceutically acceptable salt” means any non-toxic salt that, upon administration to a recipient, is capable of providing, either directly or indirectly, a compound of this invention. A “pharmaceutically acceptable counterion” is an ionic portion of a salt that is not toxic when released from the salt upon administration to a recipient.

Acids commonly employed to form pharmaceutically acceptable salts include inorganic acids such as hydrogen bisulfide, hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid and phosphoric acid, as well as organic acids such as para-toluenesulfonic acid, salicylic acid, tartaric acid, bitartaric acid, ascorbic acid, maleic acid, besylic acid, fumaric acid, gluconic acid, glucuronic acid, formic acid, glutamic acid, methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, lactic acid, oxalic acid, para-bromophenylsulfonic acid, carbonic acid, succinic acid, citric acid, benzoic acid and acetic acid, as well as related inorganic and organic acids. Such pharmaceutically acceptable salts thus include sulfate, pyrosulfate, bisulfate, sulfite, bisulfite, phosphate, monohydrogenphosphate, dihydrogenphosphate, metaphosphate, pyrophosphate, chloride, bromide; iodide, acetate, propionate, decanoate, caprylate, acrylate, formate, isobutyrate, caprate, heptanoate, propiolate, oxalate, malonate, succinate, suberate, sebacate, fumarate, maleate, butyne-1,4-dioate, hexyne-1,6-dioate, benzoate, chlorobenzoate, methylbenzoate, dinitrobenzoate, hydroxybenzoate, methoxybenzoate, phthalate, terephthalate, sulfonate, xylene sulfonate, phenylacetate, phenylpropionate, phenylbutyrate, citrate, lactate, β-hydroxybutyrate, glycolate, maleate, tartrate, methanesulfonate, propanesulfonate, naphthalene-1-sulfonate, naphthalene-2-sulfonate, mandelate and other salts. In one embodiment, pharmaceutically acceptable acid addition salts include those formed with mineral acids such as hydrochloric acid and hydrobromic acid, and especially those formed with organic acids such as maleic acid.

The compounds of the present invention (e.g., compounds of Formula I), may contain an asymmetric carbon atom, for example, as the result of deuterium substitution or otherwise. As such, compounds of this invention can exist as either individual enantiomers, or mixtures of the two enantiomers. Accordingly, a compound of the present invention may exist as either a racemic mixture or a scalemic mixture, or as individual respective stereoisomers that are substantially free from another possible stereoisomer. The term “substantially free of other stereoisomers” as used herein means less than 25% of other stereoisomers, preferably less than 10% of other stereoisomers, more preferably less than 5% of other stereoisomers and most preferably less than 2% of other stereoisomers are present. Methods of obtaining or synthesizing an individual enantiomer for a given compound are known in the art and may be applied as practicable to final compounds or to starting material or intermediates.

Unless otherwise indicated, when a disclosed compound is named or depicted by a structure without specifying the stereochemistry and has one or more chiral centers, it is understood to represent all possible stereoisomers of the compound.

The term “stable compounds,” as used herein, refers to compounds which possess stability sufficient to allow for their manufacture and which maintain the integrity of the compound for a sufficient period of time to be useful for the purposes detailed herein (e.g., formulation into therapeutic products, intermediates for use in production of therapeutic compounds, isolatable or storable intermediate compounds, treating a disease or condition responsive to therapeutic agents).

“D” and “d” both refer to deuterium. “Stereoisomer” refers to both enantiomers and diastereomers. “Tert” and “t-” each refer to tertiary. “US” refers to the United States of America.

The term “substituted with deuterium” means that one or more hydrogen atoms in the indicated moiety are substituted with a deuterium atom.

Therapeutic Compounds

The present invention provides a compound of Formula I:

or a pharmaceutically acceptable salt thereof, wherein:

R¹ is selected from C₁-C₆ alkyl, phenyl, a 5-10-membered heteroaryl, and a 3-10-membered heterocycloalkyl, wherein R¹ is optionally substituted with one or more substituents independently selected from halo and deuterium; and

-   -   n is 0 or an integer from 1 to 4.

In certain embodiments, n is 0. In certain other embodiments, n is 1. In certain other embodiments, n is 4.

In certain embodiments, R¹ is C₁-C₆ alkyl optionally substituted with one or more substituents independently selected from halo and deuterium. In one aspect of these embodiments, n is 0. In one aspect of these embodiments, R¹ is C₁-C₆ alkyl substituted with one or more deuterium atoms. As an example, R¹ is C₁-C₄ alkyl substituted with one or more deuterium atoms.

In certain embodiments, R¹ comprises at least one deuterium atom. In one aspect of these embodiments, n is 0. In one aspect of these embodiments, is —CD₃.

In certain embodiments, R¹ comprises at least one fluoride atom. In one aspect of these embodiments, n is 0. In one aspect of these embodiments, R¹ is —CF₃.

In certain embodiments, R¹ is selected from —CH₃, —CD₃ and CF₃. In one aspect of these embodiments, n is 0 or 4.

In yet another embodiment, the group

in Formula I is selected from

For example, the group

may be selected from

In yet another embodiment, the compound is selected from any one of

or a pharmaceutically acceptable salt of any of the foregoing.

In another set of embodiments, any atom not designated as deuterium in any of the embodiments set forth above is present at its natural isotopic abundance.

In another embodiment, the compound is compound 103, or a pharmaceutically acceptable salt therein, wherein any atom not designated as deuterium is present at its natural isotopic abundance, and wherein the percentage of deuterium incorporation at each position designated as deuterium is at least 95%, more particularly at least 97%, even more particularly at least 99%, yet more particularly at least 99.5%.

The synthesis of compounds of Formula I may be readily achieved by synthetic chemists of ordinary skill by reference to the Exemplary Synthesis and Examples disclosed herein.

Exemplary Synthesis

Scheme 1 illustrates an exemplary preparation of a compound of Formula I. As shown in Scheme 1, optionally deuterated niacin 1 is treated with R¹—SO₂NH₂ 2a, 2b or 2c in a manner analogous to the one described by Asaki, T. et al., Biorg. Med. Chem. 2007, 15, p. 7720 to provide a compound of Formula I wherein R¹ is CH₃, CD₃ or CF₃, respectively.

2a and 2c are commercially available. As shown in Scheme 2 below, 2b may be prepared from commercially available 3 according to the procedure described by Uno et al., Spectrochim. Acta 1975, 31A, 1217-25.

As an example, 1 in Scheme 1 may be niacin (1a) or commercially available deuterated niacin 1b, 1c or 1d:

As another example, 1 may be deuterated niacin 1e or 1f:

1e and 1f are each prepared as described by Clark, B. R., J. Labeled Compounds Radiopharm. 1976, 12, 535-40. 1e is prepared by reducing commercially available 4 with D₂ as shown in Scheme 3a below, while 1f is prepared by treating 1a with palladium acetate and poly(N-vinylpyrrolidine) followed by quenching with D₂O as shown in Scheme 3b.

The specific approaches and compounds shown above are not intended to be limiting. The chemical structures in the schemes herein depict variables that are hereby defined commensurately with chemical group definitions (moieties, atoms, etc.) of the corresponding position in the compound formulae herein, whether identified by the same variable name (i.e., R¹, R², R³, etc.) or not. The suitability of a chemical group in a compound structure for use in the synthesis of another compound is within the knowledge of one of ordinary skill in the art.

Additional methods of synthesizing compounds of Formula I and their synthetic precursors, including those within routes not explicitly shown in schemes herein, are within the means of chemists of ordinary skill in the art. Synthetic chemistry transformations and protecting group methodologies (protection and deprotection) useful in synthesizing the applicable compounds are known in the art and include, for example, those described in Larock R, Comprehensive Organic Transformations, VCH Publishers (1989); Greene, T W et al., Protective Groups in Organic Synthesis, 3^(rd) Ed., John Wiley and Sons (1999); Fieser, L et al., Fieser and Fieser's Reagents for Organic Synthesis, John Wiley and Sons (1994); and Paquette, L, ed., Encyclopedia of Reagents for Organic Synthesis, John Wiley and Sons (1995) and subsequent editions thereof.

Combinations of substituents and variables envisioned by this invention are only those that result in the formation of stable compounds.

Compositions

The invention also provides pyrogen-free pharmaceutical compositions comprising an effective amount of a compound of Formula I (e.g., including any of the formulae herein), or a pharmaceutically acceptable salt of said compound; and a pharmaceutically acceptable carrier. The carrier(s) are “acceptable” in the sense of being compatible with the other ingredients of the formulation and, in the case of a pharmaceutically acceptable carrier, not deleterious to the recipient thereof in an amount used in the medicament.

Pharmaceutically acceptable carriers, adjuvants and vehicles that may be used in the pharmaceutical compositions of this invention include, but are not limited to, ion exchangers, alumina, aluminum stearate, lecithin, scrum proteins, such as human serum albumin, buffer substances such as phosphates, glycine, sorbic acid, potassium sorbate, partial glyceride mixtures of saturated vegetable fatty acids, water, salts or electrolytes, such as protamine sulfate, disodium hydrogen phosphate, potassium hydrogen phosphate, sodium chloride, zinc salts, colloidal silica, magnesium trisilicate, polyvinyl pyrrolidone, cellulose-based substances, polyethylene glycol, sodium carboxymethylcellulose, polyacrylates, waxes, polyethylene-polyoxypropylene-block polymers, polyethylene glycol and wool fat.

If required, the solubility and bioavailability of the compounds of the present invention in pharmaceutical compositions may be enhanced by methods well-known in the art. One method includes the use of lipid excipients in the formulation. See “Oral Lipid-Based Formulations: Enhancing the Bioavailability of Poorly Water-Soluble Drugs (Drugs and the Pharmaceutical Sciences),” David J. Hauss, ed. Informa Healthcare, 2007; and “Role of Lipid Excipients in Modifying Oral and Parenteral Drug Delivery: Basic Principles and Biological Examples,” Kishor M. Wasan, ed. Wiley-Interscience, 2006.

Another known method of enhancing bioavailability is the use of an amorphous form of a compound of this invention optionally formulated with a poloxamer, such as LUTROL™ and PLURONIC™ (BASF Corporation), or block copolymers of ethylene oxide and propylene oxide. See U.S. Pat. No. 7,014,866; and United States patent publications 20060094744 and 20060079502.

The pharmaceutical compositions of the invention include those suitable for oral, rectal, nasal, topical (including buccal and sublingual), vaginal or parenteral (including subcutaneous, intramuscular, intravenous and intradermal) administration. In certain embodiments, the compound of the formulae herein is administered transdermally (e.g., using a transdermal patch or iontophoretic techniques). Other formulations may conveniently be presented in unit dosage form, e.g., tablets, sustained release capsules, and in liposomes, and may be prepared by any methods well known in the art of pharmacy. See, for example, Remington: The Science and Practice of Pharmacy, Lippincott. Williams & Wilkins, Baltimore, Md. (20th ed. 2000).

Such preparative methods include the step of bringing into association with the molecule to be administered ingredients such as the carrier that constitutes one or more accessory ingredients. In general, the compositions are prepared by uniformly and intimately bringing into association the active ingredients with liquid carriers, liposomes or finely divided solid carriers, or both, and then, if necessary, shaping the product.

In certain embodiments, the compound is administered orally. Compositions of the present invention suitable for oral administration may be presented as discrete units such as capsules, sachets, or tablets each containing a predetermined amount of the active ingredient; a powder or granules; a solution or a suspension in an aqueous liquid or a non-aqueous liquid; an oil-in-water liquid emulsion; a water-in-oil liquid emulsion; packed in liposomes; or as a bolus, etc. Soft gelatin capsules can be useful for containing such suspensions, which may beneficially increase the rate of compound absorption.

In the case of tablets for oral use, carriers that are commonly used include lactose and corn starch. Lubricating agents, such as magnesium stearate, are also typically added. For oral administration in a capsule form, useful diluents include lactose and dried cornstarch. When aqueous suspensions are administered orally, the active ingredient is combined with emulsifying and suspending agents. If desired, certain sweetening and/or flavoring and/or coloring agents may be added.

Compositions suitable for oral administration include lozenges comprising the ingredients in a flavored basis, usually sucrose and acacia or tragacanth; and pastilles comprising the active ingredient in an inert basis such as gelatin and glycerin, or sucrose and acacia.

Compositions suitable for parenteral administration include aqueous and non-aqueous sterile injection solutions which may contain anti-oxidants, buffers, bacteriostats and solutes which render the formulation isotonic with the blood of the intended recipient; and aqueous and non-aqueous sterile suspensions which may include suspending agents and thickening agents. The formulations may be presented in unit-dose or multi-dose containers, for example, sealed ampules and vials, and may be stored in a freeze dried (lyophilized) condition requiring only the addition of the sterile liquid carrier, for example water for injections, immediately prior to use. Extemporaneous injection solutions and suspensions may be prepared from sterile powders, granules and tablets.

Such injection solutions may be in the form, for example, of a sterile injectable aqueous or oleaginous suspension. This suspension may be formulated according to techniques known in the art using suitable dispersing or wetting agents (such as, for example, Tween 80) and suspending agents. The sterile injectable preparation may also be a sterile injectable solution or suspension in a non-toxic parenterally-acceptable diluent or solvent, for example, as a solution in 1,3-butanediol. Among the acceptable vehicles and solvents that may be employed are mannitol, water, Ringer's solution and isotonic sodium chloride solution. In addition, sterile, fixed oils are conventionally employed as a solvent or suspending medium. For this purpose, any bland fixed oil may be employed including synthetic mono- or diglycerides. Fatty acids, such as oleic acid and its glyceride derivatives are useful in the preparation of injectables, as are natural pharmaceutically-acceptable oils, such as olive oil or castor oil, especially in their polyoxyethylated versions. These oil solutions or suspensions may also contain a long-chain alcohol diluent or dispersant.

The pharmaceutical compositions of this invention may be administered in the form of suppositories for rectal administration. These compositions can be prepared by mixing a compound of this invention with a suitable non-irritating excipient which is solid at room temperature but liquid at the rectal temperature and therefore will melt in the rectum to release the active components. Such materials include, but are not limited to, cocoa butter, beeswax and polyethylene glycols.

The pharmaceutical compositions of this invention may be administered by nasal aerosol or inhalation. Such compositions are prepared according to techniques well-known in the art of pharmaceutical formulation and may be prepared as solutions in saline, employing benzyl alcohol or other suitable preservatives, absorption promoters to enhance bioavailability, fluorocarbons, and/or other solubilizing or dispersing agents known in the art. See, e.g.: Rabinowitz J D and Zaffaroni A C, U.S. Pat. No. 6,803,031, assigned to Alexza Molecular Delivery Corporation.

Topical administration of the pharmaceutical compositions of this invention is especially useful when the desired treatment involves areas or organs readily accessible by topical application. For topical application topically to the skin, the pharmaceutical composition should be formulated with a suitable ointment containing the active components suspended or dissolved in a carrier. Carriers for topical administration of the compounds of this invention include, but are not limited to, mineral oil, liquid petroleum, white petroleum, propylene glycol, polyoxyethylene polyoxypropylene compound, emulsifying wax, and water. Alternatively, the pharmaceutical composition can be formulated with a suitable lotion or cream containing the active compound suspended or dissolved in a carrier. Suitable carriers include, but are not limited to, mineral oil, sorbitan monostearate, polysorbate 60, cetyl esters wax, cetearyl alcohol, 2-octyldodecanol, benzyl alcohol, and water. The pharmaceutical compositions of this invention may also be topically applied to the lower intestinal tract by rectal suppository formulation or in a suitable enema formulation. Topically-transdermal patches and iontophoretic administration are also included in this invention.

Application of the subject therapeutics may be local, so as to be administered at the site of interest. Various techniques can be used for providing the subject compositions at the site of interest, such as injection, use of catheters, trocars, projectiles, pluronic gel, stents, sustained drug release polymers or other device which provides for internal access.

Thus, according to yet another embodiment, the compounds of this invention may be incorporated into compositions for coating an implantable medical device, such as prostheses, artificial valves, vascular grafts, stents, or catheters. Suitable coatings and the general preparation of coated implantable devices are known in the art and are exemplified in U.S. Pat. Nos. 6,099,562; 5,886,026; and 5,304,121. The coatings are typically biocompatible polymeric materials such as a hydrogel polymer, polymethyldisiloxane, polycaprolactone, polyethylene glycol, polylactic acid, ethylene vinyl acetate, and mixtures thereof. The coatings may optionally be further covered by a suitable topcoat of fluorosilicone, polysaccharides, polyethylene glycol, phospholipids or combinations thereof to impart controlled release characteristics in the composition. Coatings for invasive devices are to be included within the definition of pharmaceutically acceptable carrier, adjuvant or vehicle, as those terms are used herein.

According to another embodiment, the invention provides a method of coating an implantable medical device comprising the step of contacting said device with the coating composition described above. It will be obvious to those skilled in the art that the coating of the device will occur prior to implantation into a mammal.

According to another embodiment, the invention provides a method of impregnating an implantable drug release device comprising the step of contacting said drug release device with a compound or composition of this invention. Implantable drug release devices include, but are not limited to, biodegradable polymer capsules or bullets, non-degradable, diffusible polymer capsules and biodegradable polymer wafers.

According to another embodiment, the invention provides an implantable medical device coated with a compound or a composition comprising a compound of this invention, such that said compound is therapeutically active.

According to another embodiment, the invention provides an implantable drug release device impregnated with or containing a compound or a composition comprising a compound of this invention, such that said compound is released from said device and is therapeutically active.

Where an organ or tissue is accessible because of removal from the subject, such organ or tissue may be bathed in a medium containing a composition of this invention, a composition of this invention may be painted onto the organ, or a composition of this invention may be applied in any other convenient way.

In another embodiment, a composition of this invention further comprises a second therapeutic agent. The second therapeutic agent may be selected from any compound or therapeutic agent known to have or that demonstrates advantageous properties when administered with a compound having the same mechanism of action as niacin. Such agents include those indicated as being useful in combination with niacin, including but not limited to, other cholesterol lowering agents (e.g., statins, fibrates, ezetimibe, HMG-CoA reductase inhibitors, a bile acid-binding resin), anti-diabetic drugs (e.g., PPAR-gamma activators), anti-platelet agents, pain-reducing agents; prostaglandin-D2 antagonists; and prostaglandin-D2 receptor antagonists.

Preferably, the second therapeutic agent is an agent useful in the treatment or prevention of a disease or condition selected from pain, coronary artery disease, type 2 diabetes, metabolic syndrome, atherosclerosis, hypercholesterolemia, blood vessel occlusions, and dyslipidemia.

In one embodiment, the second therapeutic agent is selected from lovastatin, simvastatin, rosuvastatin, atorvastatin, ezetimibe, aspirin, laropiprant, colestipol, cholestyramine, fenofibrate, rosiglitazone, pioglitazone, clopidogrel, prednisone, oxycodone, prednisone and apple pectin, and combinations of any of the foregoing.

In another embodiment, the second therapeutic agent is selected from lovastatin, simvastatin and a combination of simvastatin and ezetimibe.

In one embodiment, the composition does not comprise a prostaglandin-D2 antagonist or a prostaglandin-D2 receptor (DP₁) antagonist.

In another embodiment, the invention provides separate dosage forms of a compound of this invention and one or more of any of the above-described second therapeutic agents, wherein the compound and second therapeutic agent are associated with one another. The term “associated with one another” as used herein means that the separate dosage forms are packaged together or otherwise attached to one another such that it is readily apparent that the separate dosage forms are intended to be sold and administered together (within less than 24 hours of one another, consecutively or simultaneously).

In the pharmaceutical compositions of the invention, the compound of the present invention is present in an effective amount. As used herein, the term “effective amount” refers to an amount which, when administered in a proper dosing regimen, is sufficient to treat the target disorder.

The interrelationship of dosages for animals and humans (based on milligrams per meter squared of body surface) is described in Freireich et al., Cancer Chemother. Rep, 1966, 50: 219. Body surface area may be approximately determined from height and weight of the subject. See, e.g., Scientific Tables, Geigy Pharmaceuticals, Ardsley, N.Y., 1970, 537.

In one embodiment, an effective amount of a compound of this invention can range from 50 mg to 2,000 mg/dose with a dosing of one to three times per day.

Effective doses will also vary, as recognized by those skilled in the art, depending on the diseases, treated, the severity of the disease, the route of administration, the sex, age and general health condition of the subject, excipient usage, the possibility of co-usage with other therapeutic treatments such as use of other agents and the judgment of the treating physician. For example, guidance for selecting an effective dose can be determined by reference to the prescribing information for niacin.

For pharmaceutical compositions that comprise a second therapeutic agent, an effective amount of the second therapeutic agent is between about 20% and 100% of the dosage normally utilized in a monotherapy regime using just that agent. Preferably, an effective amount is between about 70% and 100% of the normal monotherapeutic dose. The normal monotherapeutic dosages of these second therapeutic agents are well known in the art. See, e.g., Wells et al., eds., Pharmacotherapy Handbook, 2nd Edition, Appleton and Lange, Stamford, Conn. (2000); PDR Pharmacopoeia, Tarascon Pocket Pharmacopoeia 2000, Deluxe Edition, Tarascon Publishing, Loma Linda, Calif. (2000), each of which references are incorporated herein by reference in their entirety.

It is expected that some of the second therapeutic agents referenced above will act synergistically with the compounds of this invention. When this occurs, it will allow the effective dosage of the second therapeutic agent and/or the compound of this invention to be reduced from that required in a monotherapy. This has the advantage of minimizing toxic side effects of either the second therapeutic agent of a compound of this invention, synergistic improvements in efficacy, improved ease of administration or use and/or reduced overall expense of compound preparation or formulation.

Methods of Treatment

In one embodiment, the invention provides a method of reducing flushing and/or nausea associated with the administration of niacin to a subject comprising the step of administering to the subject an effective amount of a compound of Structural Formula I, or a pharmaceutically acceptable salt thereof in place of the niacin in the treatment. In one aspect of this embodiment, the compound of Structural Formula I, or a pharmaceutically acceptable salt thereof is not co-administered with a prostaglandin-D2 antagonist or a prostaglandin-D2 receptor (DP_(I)) antagonist.

According to another embodiment, the invention provides a method of treating a disease that is beneficially treated by niacin in a subject in need thereof, comprising the step of administering to the subject an effective amount of a compound of Structural Formula I, a pharmaceutically acceptable salt thereof, or a pharmaceutically acceptable composition of this invention. Such diseases are well known in the art and include, but are not limited to, niacin deficiency, elevated cholesterol or triglyceride levels (e.g hypercholesterolemia, dyslipidemia), reduced HDL levels, lipoprotein disorders, atherosclerosis, myocardial infarction, ischemic stroke, coronary artery disease, retinal vein occlusions, reduced blood flow and/or reduced endothelial cell function in sickle cell disease, type 2 diabetes, metabolic syndrome, diabetic, nephropathy, and pain.

In one particular embodiment, the method of this invention is used to treat a disease or condition selected from hypercholesterolemia, dyslipidemia, ischemic stroke, lipoprotein disorders, atherosclerosis, myocardial infarction, and diabetic nephropathy in a subject in need thereof.

Identifying a subject in need of such treatment can be in the judgment of a subject or a health care professional and can be subjective (e.g. opinion) or objective (e.g. measurable by a test or diagnostic method).

In another embodiment, any of the above methods of treatment comprises the further step of co-administering to the subject in need thereof one or more second therapeutic agents. The choice of second therapeutic agent may be made from any second therapeutic agent known to be useful for co-administration with niacin. The choice of second therapeutic agent is also dependent upon the particular disease or condition to be treated. Examples of second therapeutic agents that may be employed in the methods of this invention are those set forth above for use in combination compositions comprising a compound of this invention and a second therapeutic agent.

In one embodiment, the invention provides a method of reducing elevated total cholesterol or LDL-cholesterol by co-administering to a subject in need thereof a composition of the present invention and a bile acid-binding resin.

In another embodiment, the invention provides a method of reducing elevated serum triglycerides, reducing the risk of recurrent nonfatal myocardial infarction and/or promoting the regression or slowing the progression of atherosclerosis by co-administering to a subject in need thereof a composition of the present invention and, a bile acid-binding resin.

In yet another embodiment, the invention provides a method of increasing high-density lipoprotein cholesterol (HDL-C) and/or decreasing total and/or low-density lipoprotein cholesterol (LDL-C), ApoB and triglyceride levels by co-administering to a subject in need thereof a composition of the present invention and a statin.

In still another embodiment, the invention provides a method of treating a lipoprotein disorder by co-administering to a subject in need thereof a composition of the present invention and a second therapeutic agent selected from lovastatin and simvastatin.

In another set of embodiments, in any of the methods of treatment set forth above, the subject is not co-administered a prostaglandin-D2 antagonist or a prostaglandin-D2 receptor (DP₁) antagonist.

The term “co-administered” as used herein means that the second therapeutic agent may be administered together with a compound of this invention as part of a single dosage form (such as a composition of this invention comprising a compound of the invention and an second therapeutic agent as described above) or as separate, multiple dosage forms. Alternatively, the additional agent may be administered prior to, consecutively with, or following the administration of a compound of this invention. In such combination therapy treatment, both the compounds of this invention and the second therapeutic agent(s) are administered by conventional methods. The administration of a composition of this invention, comprising both a compound of the invention and a second therapeutic agent, to a subject does not preclude the separate administration of that same therapeutic agent, any other second therapeutic agent or any compound of this invention to said subject at another time during a course of treatment.

Effective amounts of these second therapeutic agents are well known to those skilled in the art and guidance for dosing may be found in patents and published patent applications referenced herein, as well as in Wells et al., eds., Pharmacotherapy Handbook, 2nd Edition, Appleton and Lange, Stamford, Conn. (2000); PDR Pharmacopoeia, Tarascon Pocket Pharmacopoeia 2000, Deluxe Edition, Tarascon Publishing, Loma Linda, Calif. (2000), and other medical texts. However, it is well within the skilled artisan's purview to determine the second therapeutic agent's optimal effective-amount range.

In one embodiment of the invention, where a second therapeutic agent is administered to a subject, the effective amount of the compound of this invention is less than its effective amount would be where the second therapeutic agent is not administered. In another embodiment, the effective amount of the second therapeutic agent is less than its effective amount would be where the compound of this invention is not administered. In this way, undesired side effects associated with high doses of either agent may be minimized. Other potential advantages (including without limitation improved dosing regimens and/or reduced drug cost) will be apparent to those of skill in the art.

In yet another aspect, the invention provides the use of a compound of Formula I alone or together with one or more of the above-described second therapeutic agents in the manufacture of a medicament, either as a single composition or as separate dosage forms, for treatment or prevention in a subject of a disease, disorder or symptom set forth above. Another aspect of the invention is a compound of Formula I for use in the treatment or prevention in a subject of a disease, disorder or symptom thereof delineated herein.

EXAMPLES Example 1 Synthesis of N-(Methylsulfonyl)Nicotinamide (Compound 100)

N-(methylsulfonyl)nicotinamide (Compound 100). Nicotinic acid (1.0 g, 8.12 mmol) was dissolved in tetrahydrofuran (16 mL) and oxalyl chloride (0.780 mL, 8.94 mmol) was added dropwise. Immediate effervescence was observed followed by precipitation of a white solid at the end of the addition. One drop of dimethylformamide was added and the reaction was allowed to stir at ambient temperature for thirty minutes. In a separate flask a solution of methyl sulfonamide (2a, 0.772 g, 8.12 mmol), triethylamine (1.47 mL, 10.55 mmol) and tetrahydrofuran (16 mL) was prepared. This solution was added to the solution of acyl chloride dropwise. The reaction was warmed at 40° C. for 72 h. The reaction was then cooled and concentrated to give an orange semisolid from which the product was triturated with dichloromethane. The resulting solid was recrystallized from methanol and dichloromethane. The desired product was obtained as a white powder (0.440 g, 27% yield). ¹H NMR (400 MHz, d₆-DMSO): δ 9.09 (br s, 1H), 8.84 (br s, 1H), 8.36-8.32 (m, 1H), 7.64-7.60 (m, 1H), 3.41 (s, 3H). MS (M+H): 201.1.

Example 2 Synthesis of 2,4,5,6-Tetradeutero-N-(methylsulfonyl)nicotinamide (Compound 103)

2,4,5,6-tetradeutero-N-(methylsulfonyl)nicotinamide (Compound 103). 2,4,5,6-tetradeutero-nicotinic acid (0.1 g, 0.787 mmol, CDN Isotopes, 98 atom % D) was dissolved in dimethylformamide (3.15 mL) and carbonyl diimidazole (0.140 g, 0.865 mmol) was added in a single portion. The reaction was heated at 40° C. for thirty minutes. Methyl sulfonamide 2a (0.082 g, 0.865 mmol) was added followed by 1,8-diazabicyclo[5.4.0]undec-7-ene (0.129 mL, 0.865 mmol). The reaction was stirred at ambient temperature until deemed complete by TLC analysis. The reaction mixture was concentrated in vacuo and the resulting residue loaded onto a silica gel pre-column. Purification by silica gel column chromatography on an ISCO system (0-100% ethyl acetate/heptanes then 0-20% methanol/dichloromethane) afforded the desired product 103 as an off-white solid (0.14 g, 0.583 mmol, 74% yield). NMR (400 MHz, CDCl₃): δ 3.48 (s, 3H). ²H NMR (400 MHz, CHCl₃): δ 9.09 (br s, 1H), 8.84 (br s, 1H), 8.36-8.32 (m, 1H), 7.64-7.60 (m, 1H). MS (M+H): 205.1.

Notable in the ¹H-NMR spectrum above was the absence of peaks in the aromatic region at around 6-10 ppm indicating an absence of hydrogen at the 2,4,5, and 6 positions of the nicotimamide ring.

Example 3 Evaluation of Metabolic Stability in Human Liver Microsomes

Microsomal Assay: Human liver microsomes (20 mg/mL) are obtained from Xenotech, LLC (Lenexa, Kans.). β-nicotinamide adenine dinucleotide phosphate, reduced form (NADPH), magnesium chloride (MgCl₂), and dimethyl sulfoxide (DMSO) are purchased from Sigma-Aldrich.

Determination of Metabolic Stability: 7.5 mM stock solutions of test compounds are prepared in DMSO. The 7.5 mM stock solutions are diluted to 12.5-50 μM in acetonitrile (ACN). The 20 mg/mL human liver microsomes are diluted to 0.625 mg/mL in 0.1 M potassium phosphate buffer, pH 7.4, containing 3 mM MgCl₂. The diluted microsomes are added to wells of a 96-well deep-well polypropylene plate in triplicate. A 10 μL aliquot of the 12.5-50 μM test compound is added to the microsomes and the mixture is pre-warmed for 10 minutes. Reactions are initiated by addition of pre-warmed NADPH solution. The final reaction volume is 0.5 mL and contains 0.5 mg/mL human liver microsomes, 0.25-1.0 μM test compound, and 2 mM NADPH in 0.1 M potassium phosphate buffer, pH 7.4, and 3 mM MgCl₂. The reaction mixtures are incubated at 37° C., and 50 μL aliquots are removed at 0, 5, 10, 20, and 30 minutes and added to shallow-well 96-well plates which contain 50 μL, of ice-cold ACN with internal standard to stop the reactions. The plates are stored at 4° C. for 20 minutes after which 100 μL of water is added to the wells of the plate before centrifugation to pellet precipitated proteins. Supernatants are transferred to another 96-well plate and analyzed for amounts of parent remaining by LC-MS/MS using an Applied Bio-systems API 4000 mass spectrometer. The same procedure is followed for the non-deuterated counterpart of the compound of Formula I and the positive control, 7-ethoxycoumarin (1 μM). Testing is done in triplicate.

Data analysis: The in vitro t_(1/2)s for test compounds are calculated from the slopes of the linear regression of % parent remaining (ln) vs incubation time relationship.

in vitro t _(1/2)=0.693/k

k=−[slope of linear regression of % parent remaining (ln) vs incubation time]

Data analysis is performed using Microsoft Excel Software.

Without further description, it is believed that one of ordinary skill in the art can, using the preceding description and the illustrative examples, make and utilize the compounds of the present invention and practice the claimed methods. It should be understood that the foregoing discussion and examples merely present a detailed description of certain preferred embodiments. It will be apparent to those of ordinary skill in the art that various modifications and equivalents can be made without departing from the spirit and scope of the invention. 

1. A compound of Formula I:

or a pharmaceutically acceptable salt thereof, wherein: R¹ is selected from C₁-C₆ alkyl, phenyl, a 5-10-membered heteroaryl, or a 3-10-membered heterocycloalkyl, wherein R¹ is optionally substituted with one or more substituents independently selected from halo and deuterium; and n is 0 or an integer from 1 to
 4. 2. The compound of claim 1, wherein R¹ is C₁-C₆ alkyl optionally substituted with one or more substituents independently selected from halo and deuterium.
 3. The compound of claim 2, wherein n is
 0. 4. The compound of claim 3, wherein R¹ is C₁-C₆ alkyl substituted with one or more deuterium atoms.
 5. The compound of claim 1, wherein R¹ is selected from —CH₃, —CD₃ and —CF₃.
 6. The compound of claim 1, wherein R¹ comprises at least one deuterium atom.
 7. The compound of claim 1, wherein n is
 0. 8. The compound of claim 1, wherein the compound is selected from

or a pharmaceutically acceptable salt thereof.
 9. The compound of claim 8, wherein any atom not designated as deuterium is present at its natural isotopic abundance.
 10. A pyrogen-free pharmaceutical composition comprising an effective amount of the compound of claim 1, or a pharmaceutically acceptable salt thereof; and a pharmaceutically acceptable carrier.
 11. The composition of claim 10, additionally comprising a second therapeutic agent selected from a steroid; a cholesterol lowering agent; an anti-diabetic agent; an anti-platelet agent; a pain-reducing agent; a prostaglandin-D2 antagonist; and a prostaglandin-D2 receptor antagonist.
 12. The composition of claim 11, wherein the second therapeutic agent is selected from lovastatin, simvastatin, rosuvastatin, atorvastatin, ezetimibe, aspirin, laropiprant, colestipol, cholestyramine, fenofibrate, rosiglitazone, pioglitazone, clopidogrel, prednisone, oxycodone, prednisone and apple pectin, and combinations of any of the foregoing.
 13. The composition of claim 10, comprising a second therapeutic agent selected from lovastatin, simvastatin and a combination of simvastatin and ezetimibe.
 14. A method of reducing flushing and/or nausea associated with the administration of niacin to a subject comprising the step of administering to the subject an effective amount of a compound of claim 1, or a pharmaceutically acceptable salt thereof in place of the niacin in the treatment.
 15. The method of claim 14, wherein the compound or pharmaceutically acceptable salt thereof is not co-administered with a prostaglandin-D2 antagonist or a prostaglandin-D2 receptor (DP₁) antagonist.
 16. A method of treating a disease or condition selected from niacin deficiency, elevated cholesterol or triglyceride levels (e.g hypercholesterolemia, dyslipidemia), reduced HDL levels, lipoprotein disorders, atherosclerosis, myocardial infarction, ischemic stroke, coronary artery disease, retinal vein occlusions, reduced blood flow and/or reduced endothelial cell function in sickle cell disease, type 2 diabetes, metabolic syndrome, diabetic nephropathy, and pain in a subject comprising the step of administering to the subject a compound of claim
 1. 17. The method of claim 16, wherein the disease or condition is selected from hypercholesterolemia, dyslipidemia, ischemic stroke, lipoprotein disorders, atherosclerosis, myocardial infarction, and diabetic nephropathy.
 18. The method of claim 16, comprising the additional step of co-administering to the subject in need thereof a second therapeutic agent.
 19. The method of claim 18, wherein the second therapeutic agent is selected from a steroid; a cholesterol lowering agent; an anti-diabetic agent; an anti-platelet agent; a pain-reducing agent; a prostaglandin-D2 antagonist; and a prostaglandin-D2 receptor antagonist.
 20. The method of claim 19, wherein the second therapeutic agent is selected from lovastatin, simvastatin, rosuvastatin, atorvastatin, ezetimibe, aspirin, laropiprant, colestipol, cholestyramine, fenofibrate, rosiglitazone, pioglitazone, clopidogrel, prednisone, oxycodone, prednisone and apple pectin, and combinations of any of the foregoing.
 21. The method of claim 20, wherein the condition is selected from elevated total cholesterol, elevated LDL-cholesterol, elevated serum triglycerides, risk of recurrent non-fatal myocardial infarction and/or atherosclerosis; and the subject is co-administered a bile acid-binding resin.
 22. The method of claim 20, wherein the condition is selected from reduced high-density lipoprotein cholesterol (HDL-C), elevated total cholesterol, elevated low-density lipoprotein cholesterol (LDL-C), elevated ApoB and elevated triglyceride levels; and the subject is co-administered a statin.
 23. The method of claim 20, wherein the condition is a lipoprotein disorder; and the subject is co-administered a second therapeutic agent selected from lovastatin and simvastatin.
 24. The method of claim 16, wherein the subject is not co-administered a prostaglandin-D2 antagonist, or a prostaglandin-D2 receptor (DP₁) antagonist. 